1. Field of the Invention
The present invention relates to a method of manufacturing a bonded semiconductor substrate and a dielectric isolated bipolar transistor and, more specifically, to a method of manufacturing a bonded semiconductor substrate using a substrate bonding technique and a method of forming a dielectric isolated high-speed bipolar transistor on the bonded semi-conductor substrate.
2. Description of the Related Art
A dielectric isolated bipolar device having an SOI (silicon on insulator) structure has recently been proposed as a means for increasing the operation speed of a silicon bipolar transistor in order to reduce a junction capacitance between devices and between a collector and a substrate.
A bonded semiconductor substrate having the SOI structure is manufactured by the following one conventional method. A silicon oxide film is formed on the surface of one of two semiconductor wafers or each surface of the two wafers, and the wafers are bonded by high-temperature heat treatment with the surfaces in contact with each other. After that, one of the bonded wafers is polished from the backside thereof and then etched.
The above method however has a drawback wherein the thickness of an SOI film of the bonded semiconductor wafers varies with the polishing and etching. The variation in thickness varies the depth of a collector layer of the finished transistor, which makes it difficult to control the resistance of the collector layer. The reduction in collector resistance is important for the high-speed operation of a bipolar transistor. Though it is advantageous to use a thin epitaxial growth layer to decrease the collector resistance, a variation in collector resistance is fatal to uniform formation of high-speed devices.
A method of forming the above dielectric isolated bipolar transistor on the conventional bonded semiconductor substrate has the drawback wherein the depth of the collector layer are varied with the uneven thickness of the SOI film, thereby making it difficult to control the collector resistance and to uniformly form the high-speed devices.